Symmetric cryptography is a cryptography method in which both the encryption and decryption operations share the same key (or, less commonly, in which their keys are different, but related in an easily computable way). Examples of symmetric cryptography algorithms include Data Encryption Standard (DES) and Advanced Encryption Standard (AES).
On the other hand, public key encryption algorithms use asymmetric keys for encryption and decryption. The asymmetric keys comprise a private key (which is held only by its owner) and a public key (which is available to other entities). The two keys are separate but complementary in function. Information that is encrypted with the public key can be decrypted only with the corresponding private key. The two keys together are called a key pair or a key set. RSA algorithm is an example of public key encryption algorithms.
Encrypting File System (EFS) is a file system with encryption services. The technology transparently allows files to be encrypted and decrypted on a file system to protect confidential data from attackers with physical access to the computer. An EFS uses public key cryptography to ensure that decrypting a file without a correct key is in theory impossible, or requires an unreasonable length of time to crack.
An EFS works by encrypting a file with a symmetric key, also known as File Encryption Key (FEK). The FEK is then encrypted with a public key that is usually associated with a user and is available to third parties. To decrypt the encrypted file, the EFS uses a private key, accessed only by the user, to decrypt the encrypted FEK. The EFS then decrypts the file which is encrypted with the FEK. In general, these encryption and decryption operations are performed at a layer below an operating system so that it is transparent to users and to applications running thereon.